Immunochemical analysis of a photoreceptor protein using anti-IP3 receptorantibody in the unicellular organism, Blepharisma

The blepharismin-200 kD protein complex of the ciliated protozoan Blepharis ma is a novel type of photosensor responsible for the step-up photophobic r esponse of the cell. In immunoblotting assays, the 200 kD protein is weakly cross-reacted with anti-inositol triphosphate receptor antibody (anti-IP3 R antibody). Indirect immunofluorescence assays show that the pigment granu les in which the blepharismin-200 kD protein complex is localized are label led by anti-IP3 R antibody. When the anti-IP3 R antibody or antisense oligo nucleotide for IP3 receptor is introduced into the living cells of Blephari sma, both the photosensitivity of the cells and content of blepharismin-200 kD protein are reduced. The results suggest that the photoreceptor 200 kD protein is possibly an IP3 receptor-like protein. (C) 2000 Elsevier Science S.A. All rights reserved.